If you say borei isvei vesamim or borei atzei vesamim, you should say the blessing again once you have had a lapse of thought (hesech da'at); that is, once you have stopped thinking about smelling fragrances at that time.

“Cessation of intention” (hesech da'at) can occur when you get involved in a different action or activity than what you were doing. It is not time dependent.

If you said or heard the blessing borei pri ha'gafen, finished drinking had hesech da'at, and then want to make a new blessing over the remaining wine in the cup, see Borei Pri HaGafen: Saying Again.

You may not do any activities while wearing tefilin that would distract you (hesech da'at) from remembering that you are wearing tefilin.
 

You may say a new blessing on any remaining wine if:

• You said, or heard someone saying, borei pri ha'gafen,
• Drank some wine (or grape juice),
• Decided to stop drinking (hesech da'at), and
• Returned to drink from the same cup later.

Because bread or mezonot REQUIRES you to say an after-blessing at the place where you ate it, you are considered to NOT have had an interruption of thought (hesech da'at ) when you move and eat more bread or mezonot at the new place, and you may say the after-blessing at the new place.
 

You may continue eating without saying a new fore-blessing--without a time limit--as long as you are not involved in some other activity that distracts you from eating (hesech da'at). 

You must eat a second meal on Jewish festival (or Shabbat) day with 1.9 fl. oz., or 56 ml, of bread--even if you already said ha'motzi and ate bread at kiddush.

If you fell asleep for more than 30 minutes in the middle of a meal:

• Wash again and say ha'motzi again, and then say birkat ha'mazon, OR 
• Eat other items with a fore-blessing and after-blessing (since your previous eating is finished).

• Say birkat ha'mazon if you are:
  • Finished eating, and
  • Not hungry again, after having been satiated at the meal.
• Do not say birkat ha'mazon if you are
  • Finished eating, and
  • Hungry again (after having been satiated at the meal), as the original snack or meal is irrelevant to any after-blessing now.

If you fell asleep for more than 30 minutes in the middle of a meal:
Step 1: Wash your hands the Three-Times Method to remove the tum'a of your sleep.
Step 2a: To Continue Eating
To continue eating in this case, since the previous blessings and food are no longer relevant (due to hesech da'at), you may:

• Wash again and say ha'motzi again, and then say birkat ha'mazon, OR 
• Eat other items with a fore-blessing and after-blessing (since your previous eating is finished).

Step 2b: If You Are Finished Eating

• Say birkat ha'mazon if you are:
  • Finished eating, and
  • Not hungry again, after having been satiated at the meal.
• Do not say birkat ha'mazon if you are
  • Finished eating, and
  • Hungry again (after having been satiated at the meal), as the original snack or meal is irrelevant to any after-blessing now.

The fore-blessing (bracha rishona) must be said where you eat.  However, sometimes you may begin eating in one domain and continue eating in another domain. A domain may be any physically limited area (car, house, restaurant, office building) or the outdoors (highway, park, etc.). Once you left the first place, you are considered to have had an interruption of thought (hesech da'at) and are no longer eating that original snack or meal. 
Whether you say a new fore-blessing depends on your intention when you said the fore-blessing:

• Do not say a new fore-blessing if you had intended to go to the second place, as long as the food at the second place is in the same food categories as what you already blessed on at the first place.
• Say a new fore-blessing if you had not intended to continue eating in the second domain, even if you had planned to return to that first place and continue eating.
  Exception You do not need to make a new fore-blessing if:

  • You return to the first place and even one person who was eating with you is still there, OR
  • You had eaten bread or mezonot and then left but had not said the after-blessings of birkat ha'mazon or al ha'michya, even if no one is left from before.
    Reason Since you are required to say birkat ha'mazon or al ha'michya, you are still considered to be continuing your meal.

    Note As long as you are under the same roof, do not say new blessings on food at the new place (such as when switching seats or even rooms in a restaurant).

    Exception Even if you washed your hands and said ha'motzi at the first place, say a new blessing on food that would have required a new blessing at the first place, such as new wine or any dessert other than mezonot.

If you take off your tefilin because you have to, such as to go to the bathroom, or if one or both of the tefilin fall or slide off your arm or head, say: 

• Both blessings again when you replace the head tefila (tefila shel rosh) on your head.
• Only the first blessing when replacing the arm tefila (tefila shel yad) on your arm.
• Each blessing in its correct place if you took off both.

Categories of Batel/Nullification
Categories of nullification of non-kosher ingredients:

• Never batel.
• Batel b'shishim when the non-kosher substance is less than 1/60th of the total volume of the food.
• Batel barov when the non-kosher substance is less than 1/2 of the total volume of the food.

When Can a Non-Kosher Substance Be Nullified in a Mixture?
Whether a non-kosher substance can be nullified in a mixture depends on 3 factors:

• Whether the owner is Jewish;
• Whether the intended eaters are Jewish; and
• Whether the non-kosher substance was added intentionally as non-kosher.

If the answers to all three cases is yes, the food is never batel.

Food “Nullified in 60 Parts”:
Accidentally Adding Non-Kosher to Kosher Food 

• Less than 1/60 of the volume of the whole.
• Mixed in and not lying on the surface.
• Not intentionally added by a Jew.
• Not listed in “Foods that Never Become Nullified” (below).

Min b'Mino
Substances are only batel when they are similar (“min b'mino”). The substances must be the same type, have the same taste, and have the same appearance (the eater cannot identify them as being different).
Note In such situations, it would be batel barov from Torah (d'oraita) but batel b'shishim (1/60^th) by rabbinical order (d'rabanan).
Example A piece of non-kosher meat is mixed in with kosher meat of more than 60 times the volume of the non-kosher piece. The non-kosher meat is batel b'shishim.
Note As a practical matter, this can only apply to ground meat.
Counter Example Non-kosher chocolate syrup or a non-kosher flavored extract mixed into milk or other liquid or onto a solid would NOT be min b'mino even though both are liquids, since their appearances, flavors, and substance are different.

Too Thin To Make Non-Kosher

• Yayin Nesech
  Wine that has been offered to a pagan god or used for idolatrous purposes (yayin nesech) is forbidden in any amount!
• Mixtures of Milk and Meat
  Mixtures of milk and meat are not ever batel if they were cooked together.
  ExceptionBatel in 1/60^th if:
  • You cannot identify either substance AND
  • The mixture is liquid in liquid or solid mixed with solid.

Examples: Milk from a pig mixed with milk from a cow; ground kosher meat mixed in with ground non-kosher meat.

• Chametz

• Jew Intentionally Adding Non-Kosher Item

• Unflavored or Flavored Non-Kosher Ingredient
  
  Non-Jew Adds Unflavored Non-Kosher Ingredient
  

  Situation A non-Jew adds a non-kosher ingredient that has no flavor. 
  Status The non-kosher ingredient is nullified if less than 1/2 of the total (it does not need to be less than 1/60th--batel ba'shishim).

  
  Non-Jew Adds Flavored Non-Kosher Ingredient

  Situation A non-Jew adds a flavored non-kosher ingredient even if to impart flavor.
  Status The non-kosher ingredient is nullified in 60 parts (batel ba'shishim).
  

  Note If a Jew had told the non-Jew to add the ingredient, the mixture is non-kosher, just as if a Jew had added it. 
• Stam Yeinam Added to Water
  Situation A non-Jew adds—to water--stam yeinam (uncooked/non-mevushal) wine that has been handled while open by anyone other than a shomer-Shabbat Jew.  
  Status As long as the wine is less than 1/7th of the final volume, the mixture is kosher. 

  Note For mixtures with liquids other than water, consult a rabbi. 

• Essential Additives

• Food Bought by the Piece

• Important Food

• Permissible in Future (Davar SheYesh Lo Matirin)

• An egg laid on Shabbat will not be nullified by being mixed with eggs laid before Shabbat.
• Matza made of chadash flour will not be nullified by being mixed with matza made from yashan flour.

• Whole Insects

• Frozen or raw chopped or ground vegetables or spices may be considered kosher even without supervision.
  Reason We assume that any bugs in the food would have gotten partly chopped or disintegrated and therefore nullified.
• If a recipe calls for chopping or grinding herbs or vegetables, you may do so without first checking them for bugs.
  Note However, if you know there are bugs, you may not chop the food for the purpose of making the bugs nullified:  You must still check for insects before cooking or eating the food and if you see any bugs, you must remove them.