Changing the order of how the food and liquid are usually placed in: [This depends on how the mixture is normally made in ones area]. If in ones areas during the week the custom is that the vinegar is placed first [and then the flour is placed], then [on Shabbos] one first places the flour [in the bowl] and afterwards places the vinegar.
In a place that they are accustomed that the flour be placed first [and then the vinegar], on Shabbos one first places the vinegar in [and then the flour]. [See Q&A]
Changing the form of mixing: In addition to the above mentioned change, one is also required to mix it with an irregularity. This is defined as using ones hand to mix it or shaking the vessel, as opposed to using a spoon.
Summary-The definition of an irregularity:
Although it is permitted to knead a thin batter one is required to make two changes from the normal way one kneads during the week. These are:
- Changing the order of ingredients. If in ones areas during the week the custom is that the liquid is placed first and then the food is placed, on Shabbos one first places the food and afterwards places the liquid. If the custom is vice versa, on Shabbos one first places in the liquid and then the food.
- Changing the mixing method: In addition to the above, one may not blend the mixture with a spoon. One is rather to do so with his hands or through shaking the vessel [or through pouring the food from one vessel to another] until it mixes in.
What does one do if he does not know the order of which a certain mixture is mixed?
Some Poskim rule if one does not know what the custom is he is to first place in the food and then the liquid. Other Poskim rule if one does not know the custom he is not allowed to knead the mixture.
If one is unable to mix the mixture together using his fingers or bowl may he use a spoon?
Yes. Although he is to do so by making alternative strokes vertical and horizontal as opposed to in circular motion. Likewise he is to remove the spoon between each stroke. From the letter of the law however removing the spoon between each stroke is unnecessary so long as he is careful not to make a circular motion with the spoon.
May one use an irregular vessel to mix the ingredients?
- Example: May one use a knife, the back of a spoon or fork, to mix the mixture?
It is allowed to use an irregular item, such as a knife to mix the ingredients, although one may not mix the ingredients in a fast pace. Likewise one may use a common vessel in an irregular way, such as the back of a spoon or fork.
May one blend the mixture quickly when using his hands to mix?
Seemingly this is permitted.
List of forms of irregularities:
- Kneading little by little.
- Switching order of the foods.
- Mixing with a finger or the back of a spoon or fork.
Making vertical and horizontal strokes with a spoon.
To note however that this form of change was only required if one were to make a lot at a time. If however one were to make a little at a time, then that itself [the fact that he is only making a little at a time] is considered an irregularity. [See Halacha 2A above, as well as 324/3 in the first opinion] Vetzaruch Iyun why this option of making a little at a time was not mentioned in the second opinion [neither here nor in 324/3] as well as with regards to Charoses [brought below Halacha 5]. As well Tzaruch Iyun why this option of irregularity was not mentioned either by the Ketzos Hashulchan or SSH”K. Seemingly this option does not hold true in accordance to the second opinion as it only helps when making an item into a thick batter, which is always forbidden according to the second opinion, Vetzaruch Iyun. See Igros Moshe 4/74 Lash for a summary of the different forms of irregularities.
 473/34 regarding making Charoses, based on Rama, brought in Ketzos Hashulchan 130/3 and footnote 5.
 Regarding why Admur writes that a spoon may be used by the case of mustard, see next Halacha and the footnote there!
 Admur 473/34; Rama 321/16
Other Opinions: Chazon Ish 58/5 rules by a thin batter one is only required to make one change from the way it is done during the week, such as to place the ingredients in differently, although he may mix it normally with a spoon.
 Above Halacha 16
 Ketzos Hashulchan 130/2; Mishneh Berurah 321/57
 Taz 321/11; Chazon Ish 58/1; See Bris Olam Lash
 SSH”K 8/9 based on ruling in 324/3: One may knead even a lot at a time although taking care to not mix it with ones hands after placing the water in it as is the usual way that one mixes it during the week. Rather one is to mix it with a large serving spoon or a stick which contains a horizontal piece of wood on it, even many times until it mixes well. This is considered an irregularity since he is not mixing it with his hands and is not circling the spoon or wooden stick in its usual form as done during the week, but rather is mixing it by pushing it horizontally and vertically; therefore this is considered a complete irregularity.
 Seemingly Rav Farkash learns that this may be done even initially, as he rules regarding kneading egg salad with oil that it may be mixed in this method. There he mentions it is proper to remove the spoon in between each stroke. [Shabbos Kehalacha 7/61] Nevertheless in Piskeiy Teshuvos 321/9 he learns this method is only to be done in a time of need.
 Shabbos Kehalacha 7/61 and so questions Chazon Ish and so rules Bris Olam. The reason for this requirement is so one not come to make a circular motion accidently when mixing.
 Igros Moshe 4/74 Lash 10
 Igros Moshe 4/74 Lash 11; Minchas Yitzchak 1/74
 On the one hand Admur writes in Halacha 5 below that when adding liquid to the mustard one may only mix in slowly. However regarding Charoses he does not make mention of this. On the one hand one can explain that by Charoses he relied on what he already explained in this chapter, although this is difficult to accept being that he does make mention of the other forms of irregularity so why would he omit this one. As well the end of the case regarding mustard is discussing using a spoon to mix, and perhaps the ending of “not to mix quickly” is going on when a spoon is used. As well it seems unlikely that 3 irregularities would be required. It is also implied from all Poskim which mention using the finger and do not limit this to being done slowly, that it is allowed.
 See Igros Moshe 4/74 Lash for a summary and explanation behind the different forms of irregularities.